Recently, a super-resolution technology for observing a sample with a higher solution than the resolution of a microscopic optical system has been proposed (Patent Document 1, etc.). The Patent Document 1 discloses a structured illuminating method for exposing a sample to structured-illumination to generate a modulated image, detecting a modulated image at plural times with an image sensor while changing the phase of the structured-illumination, and demodulating these modulated images by a calculation, thereby obtaining a super-resolved image.
A recess portion called as a missing cone exists in the neighborhood of the zero spatial frequency of a transfer function of a normal microscopic optical system. Therefore, with respect to a pattern having low spatial frequencies contained in the sample, it is impossible to decompose the pattern in the optical axis direction and observe the pattern concerned. However, according to the structured illuminating method, the transfer function is substantially enlarged (the transfer function concerned corresponds to that obtained by displacing the transfer function of the microscopic optical system by only the spatial frequency of the structure illumination and superposing thus obtained transfer functions), and thus if the spatial frequency of the structured illumination is merely properly set, it would be expected that the missing cone is eliminated and high-resolution observation in the optical axis direction can be performed.
Patent Document 1: Japanese Unexamined Patent Application Publication No. Hei11-242189